A histogram shows how often values fall into different ranges. Each bar covers a bin — a range of numbers like “20 up to (but not including) 30”, written [20, 30).

• The height of a bar tells you how many values fall in its bin.
• Each value belongs to exactly one bin. The left number is included; the right number is not. So 30 goes in [30, 40), not in [20, 30).
• The total number of values is the sum of all the bar heights.

To build a histogram from a categorized frequency table, draw one bar per row, with the bar's height matching the frequency in that row. Put the bars next to each other — they touch, because the intervals are continuous.

A histogram looks a lot like the bar graph from 2nd grade, but a histogram is for numbers, not categories. That’s why the bars touch.